(a) Field of the Invention
The present invention relates to an apparatus and a method for surveying an air flow and, more particularly, to an apparatus and a method used for measuring a direction of a laminar air flow.
(b) Description of the Related Art
Performance tests after completion of building a clean room for fabricating a semiconductor device includes an examination in which an air flow in the clean room is surveyed especially in a region of a laminar air flow. Such a survey includes a vertical test of a laminar air flow in which an angle deviation of the direction of the air flow is examined from a vertical direction. When measuring the direction of an air flow in a clean room, it is important not to disturb the original air flow.
FIG. 1 shows a typical clean room in which a vertical laminar air flow is surveyed by conventional methods. An air flow passing HEPA filters 45 is directed downward in the clean room toward an access floor 46 and passes therethrough. As shown in FIG. 1, conventional methods for measuring an angle deviation of the air flow from a vertical direction includes one in which an angle deviation of a silk string 42 hanging from the ceiling 41 in the air flow or a mist stream 44 generated from pure water by a mist generator 43 and discharged downward in the air flow is surveyed or measured with the eye. In such a conventional method, however, the air flow can be surveyed merely in a qualitative characteristic. Especially with the survey using a silk string 42, the mass of the silk string 42 itself cannot be neglected for obtaining a correct test result.
Other conventional methods for measuring a direction of a laminar air flow include one using a heat sensor acting as an air flow sensor. However, an air flow sensor which measures directly a laminar air flow having a very low velocity of, for example, 0.5 m/sec disturbs the original air flow, so that an accurate angle representing the direction of the air flow is not obtained in surveying a laminar air flow.